An attaching method for a light-amount sensor used for light-emitting control of a flash unit in cameras has been disclosed in Japanese Patent Laid-Open Publication No. 2002-122911. The description will hereinafter be given of the method with reference to FIG. 10.
The camera disclosed in Japanese Patent Laid-Open Publication No. 2002-122911 has an upper cover unit 1305 and a camera body unit 1306. The flash light (leaked light) leaking from the side of a flash panel 1124, which is attached to the upper cover unit 1305, enters an optical fiber tube 1127. The emergent portion of the optical fiber tube 1127 is glued on a coupler 1307, and fixed to a surface opposite to the camera body unit 1306 with screws.
A case 1131 is fixed to the camera body unit 1306, and a hole 1131a is formed from the case 1131 toward the upper caver unit 1305. When the upper cover unit 1305 is attached to the camera body unit 1306, the coupler 1307 is inserted into the hole 1131a. A diffusing plate (diffuser) 1132 is provided ahead of the hole 1131a, and the leaked light transmitted through the optical fiber tube 1127 illuminates the end surface 1132a of the diffusing plate 1132.
The illuminated diffusing plate 1132 emits light whose directivity is reduced by the diffusion effect, from the surface 1132b forming an angle of 90 degrees with the end surface 1132a. The case 1131 has a hole directing the emitting surface 1132b of the diffusing plate 1132, and a light-control sensor 1102 is fixed by a spring, not shown in the figure, via an infrared cut filter 1133.
In the above-described flash-light-amount detection system, since the optical paths in the upper cover unit 1305 and in the camera body unit 1306 are formed separately, the tolerance of the emergent position of the optical fiber tube 1127 becomes large. The diffusing plate 1132 has a function of absorbing the position tolerance.
However, the above-described flash-light-amount detection system includes a lot of constituent parts. Specifically, the coupler for fixing the optical fiber tube, the light-amount sensor, the diffusing plate, the case holding the diffusing plate and the spring for fixing the light-amount sensor are separately included, thereby increasing the cost of the constituent parts and fabrication totally. Consequently, the proportion of the constituent parts of the flash-light-amount detection system in the camera becomes large, thereby increasing the size of the camera.
Further, since the flash-light-amount detection system is constituted by two units which are the upper cover unit and the camera body unit, the positional tolerance becomes large, and thereby the diffusing plate is required for absorbing the positional tolerance. However, using the diffusing plate makes the light-receiving loss large. Therefore, increasing the sensitivity of the sensor is required, thereby deteriorating the S/N ratio.
In addition, since the function and operation of the flash-light-amount detection system cannot be checked independently, it is not possible to confirm whether each components of the detection system functions normally or not and whether the fabrication has finished normally or not until the upper cover unit and camera body unit are assembled. Therefore, if any trouble is detected after the assembling of the upper cover unit and camera body unit, it takes a long time to identify the trouble section and overhaul it, thereby increasing the cost.